Commissioning results of Nb3Sn cavity vapor diffusion deposition system at JLab

Abstract

Nb3Sn as a BCS superconductor with a superconducting critical temperature higher than that of niobium offers potential benefit for SRF cavities via a lower-than-niobium surface resistance at the same temperature and frequency. A Nb3Sn vapor diffusion deposition system designed for coating of 1.5 and 1.3 GHz single-cell cavities was built and commissioned at JLab. As the part of the commissioning, RF performance at 2.0 K of a single-cell 1.5 GHz CEBAF-shaped cavity was measured before and after coating in the system. Before Nb3Sn coating the cavity had a Q0 of about 10E10 and was limited by the high field Q-slope at Eacc about 27 MV/m. Coated cavity exhibited the superconducting transition at about 17.9 K. The low-field quality factor was about 5 10E9 at 4.3 K and 7 10E9 at 2.0 K decreasing with field to about 1 10E9 at Eacc about 8 MV/m at both temperatures. The highest field was limited by the available RF power.